Editing Gasoline (section)

==Chemical analysis and production==
[[File:GasolineComp.png|right|thumb|Some of the components of gasoline: [[isooctane]], [[butane]], 3-[[ethyltoluene]], and the octane enhancer [[MTBE]]]]
[[File:Nodding_donkey.jpg|thumb|A [[pumpjack]] in the United States]]
[[File:Gulf_Offshore_Platform.jpg|thumb|An [[oil rig]] in the [[Gulf of Mexico]]]]
Commercial gasoline as well as other liquid transportation fuels are complex mixtures of hydrocarbons.<ref>{{Cite web |title=Hydrocarbon Gas Liquids Explained - U.S. Energy Information Administration (EIA) |url=https://www.eia.gov/energyexplained/hydrocarbon-gas-liquids/ |access-date=2022-08-05 |website=www.eia.gov |archive-date=5 August 2022 |archive-url=https://web.archive.org/web/20220805213231/https://www.eia.gov/energyexplained/hydrocarbon-gas-liquids/ |url-status=live }}</ref> The performance specification also varies with season, requiring less volatile blends during summer, in order to minimize evaporative losses.

Gasoline is produced in [[Oil refinery|oil refineries]]. Roughly {{convert|19|U.S.gal|L|sp=us|order=flip}} of gasoline is derived from a {{convert|42|U.S.gal|L|sp=us|adj=on|order=flip}} barrel of [[crude oil]].<ref>{{cite web |author=<!--Not stated--> |date=12 August 2016 |title=Gasoline—a petroleum product |url=https://www.eia.gov/energyexplained/index.cfm?page=gasoline_home |url-status=live |archive-url=https://web.archive.org/web/20170524145355/https://www.eia.gov/Energyexplained/index.cfm?page=gasoline_home |archive-date=24 May 2017 |access-date=15 May 2017 |website=U.S. Energy Information Administration website |publisher=U.S. Energy Information Administration |df=dmy-all}}</ref> Material separated from crude oil via [[distillation]], called virgin or straight-run gasoline, does not meet specifications for modern engines (particularly the [[octane rating]]; see below), but can be pooled to the gasoline blend.

The bulk of a typical gasoline consists of a homogeneous mixture of [[hydrocarbon]]s with between four and twelve [[carbon]] atoms per molecule (commonly referred to as C4–C12).<ref name="Ullmann2">Werner Dabelstein, Arno Reglitzky, Andrea Schütze and Klaus Reders "Automotive Fuels" in ''Ullmann's Encyclopedia of Industrial Chemistry'' 2007, Wiley-VCH, Weinheim. {{doi|10.1002/14356007.a16_719.pub2}}</ref> It is a mixture of paraffins ([[alkane]]s), olefins ([[alkene]]s), napthenes ([[cycloalkane]]s), and [[aromatic]]s. The use of the term ''paraffin'' in place of the standard chemical nomenclature ''alkane'' is particular to the oil industry (which relies extensively on jargon). The composition of a gasoline depends upon:
* the oil refinery that makes the gasoline, as not all refineries have the same set of processing units;
* the [[crude oil]] feed used by the refinery;
* the grade of gasoline sought (in particular, the octane rating).

The various refinery streams blended to make gasoline have different characteristics. Some important streams include the following:
* '''Straight-run gasoline''', sometimes referred to as ''[[naphtha]] (and also light straight run naphtha "LSR" and light virgin naphtha "LVN")'', is distilled directly from crude oil. Once the leading source of fuel, naphtha's low octane rating required organometallic fuel additives (primarily [[tetraethyllead]]) prior to their phaseout from the gasoline pool which started in 1975 in the United States.<ref>{{Cite web |last=Hofverberg |first=Elin |date=2022-04-14 |title=The History of the Elimination of Leaded Gasoline {{!}} In Custodia Legis |url=https://blogs.loc.gov/law/2022/04/the-history-of-the-elimination-of-leaded-gasoline/ |access-date=2025-01-16 |website=The Library of Congress}}</ref> Straight run naphtha is typically low in aromatics (depending on the grade of the crude oil stream) and contains some cycloalkanes (naphthenes) and no olefins (alkenes). Between 0 and 20 percent of this stream is pooled into the finished gasoline because the quantity of this fraction in the crude is less than fuel demand and the fraction's [[Octane rating#Research Octane Number (RON)|Research Octane Number]] (RON) is too low. The chemical properties (namely RON and [[Reid vapor pressure]] (RVP)) of the straight-run gasoline can be improved through [[Catalytic reforming|reforming]] and [[Isomerisation|isomerization]]. However, before feeding those units, the naphtha needs to be split into light and heavy naphtha. Straight-run gasoline can also be used as a feedstock for steam-crackers to produce olefins.
* '''Reformate''', produced from straight run gasoline in a [[catalytic reformer]], has a high octane rating with high aromatic content and relatively low olefin content. Most of the [[benzene]], [[toluene]], and [[xylene]] (the so-called [[BTX (chemistry)|BTX]] hydrocarbons) are more valuable as chemical feedstocks and are thus removed to some extent. Also the BTX content is regulated.
* '''Catalytic cracked gasoline''', or catalytic cracked [[Petroleum naphtha|naphtha]], produced with a [[Fluid catalytic cracking|catalytic cracker]], has a moderate octane rating, high olefin content, and moderate aromatic content.
* '''Hydrocrackate''' (heavy, mid, and light), produced with a [[hydrocracker]], has a medium to low octane rating and moderate aromatic levels.
* '''Alkylate''' is produced in an [[alkylation]] unit, using [[isobutane]] and C3-/C4-olefins as feedstocks. Finished alkylate contains no aromatics or olefins and has a high MON ([[Motor octane number|Motor Octane Number]]) Alkylate was used during world war 2 in [[aviation fuel]].<ref>{{cite web |date=6 August 2021 |title=Alkylate: Understanding a Key Component of Cleaner Gasoline |website=[[American Fuel and Petrochemical Manufacturers]] |url=https://afpm.org/newsroom/blog/alkylate-understanding-key-component-cleaner-gasoline |access-date=21 October 2024 }}</ref> Since the late 1980s it is sold as a specialty fuel for (handheld) gardening and forestry tools with a combustion engine.<ref>{{cite web |title=Specially designed fuel for cleaner oceans |website=AlkylateFuel.com |url=https://www.alkylatefuel.com/ |access-date=21 October 2024 }}</ref><ref>{{cite web |title=The story behind Aspen Alkylate Fuel |website=AspenFuel.co.uk |date=5 June 2024 |url=https://aspenfuel.co.uk/about-aspen/#story |access-date=21 October 2024 }}</ref> 
* '''Isomerate''' is obtained by isomerizing low-octane straight-run gasoline into iso-paraffins (non-chain alkanes, such as [[isooctane]]). Isomerate has a medium RON and MON, but no aromatics or olefins.
* '''Butane''' is usually blended in the gasoline pool, although the quantity of this stream is limited by the RVP specification.
* '''[[Oxygenate]]s''' (more specifically [[Alcohol (chemistry)|alcohols]] and [[ester]]s) are mostly blended into the pool in the US as [[Ethanol fuel|ethanol]]. In Europe and other countries, the blends can contain [[Ethanol fuel|ethanol]] in addition to [[Methyl tert-butyl ether|Methyl tertiary-butyl ether]] (MTBE) and [[Ethyl tert-butyl ether]] (ETBE). MTBE in the United States was banned by most states in the early to mid 2000s.<ref>{{Cite web |last=US EPA |date=June 2004 |title=State Actions Banning MTBE (Statewide) |url=https://archive.epa.gov/mtbe/web/pdf/420b04009.pdf |website=EPA Archives}}</ref> A few countries still allow [[methanol]] as well to be blended directly into gasoline, especially in China.<ref>{{Cite web |title=China’s use of methanol in liquid fuels has grown rapidly since 2000 - U.S. Energy Information Administration (EIA) |url=https://www.eia.gov/todayinenergy/detail.php?id=30072 |access-date=2025-02-13 |website=www.eia.gov}}</ref> More about oxygenates and blending is covered further in this article.

The terms above are the jargon used in the oil industry, and the terminology varies.

Currently, many countries set limits on gasoline [[aromatic]]s in general, benzene in particular, and olefin (alkene) content. Such regulations have led to an increasing preference for alkane isomers, such as isomerate or alkylate, as their octane rating is higher than n-alkanes. In the European Union, the benzene limit is set at one percent by volume for all grades of automotive gasoline. This is usually achieved by avoiding feeding C6, in particular [[cyclohexane]], to the reformer unit, where it would be converted to benzene. Therefore, only (desulfurized) heavy virgin naphtha (HVN) is fed to the reformer unit<ref name="hedl2">{{cite journal |last1=Huess Hedlund |first1=Frank |last2=Boier Pedersena |first2=Jan |last3=Sinc |first3=Gürkan |last4=Garde |first4=Frits G. |last5=Kragha |first5=Eva K. |last6=Frutiger |first6=Jérôme |date=February 2019 |title=Puncture of an import gasoline pipeline—Spray effects may evaporate more fuel than a Buncefield-type tank overfill event |url=https://backend.orbit.dtu.dk/ws/files/160875647/1_s2.0_S0957582018306153_main.pdf |url-status=live |journal=Process Safety and Environmental Protection |volume=122 |pages=33–47 |doi=10.1016/j.psep.2018.11.007 |bibcode=2019PSEP..122...33H |archive-url=https://web.archive.org/web/20211102115932/https://backend.orbit.dtu.dk/ws/files/160875647/1_s2.0_S0957582018306153_main.pdf |archive-date=2 November 2021 |access-date=18 September 2021}}</ref>

Gasoline can also contain other [[organic compound]]s, such as [[organic ether]]s (deliberately added), plus small levels of contaminants, in particular [[organosulfur]] compounds (which are usually removed at the refinery).

On average, U.S. petroleum refineries produce about 19 to 20 gallons of gasoline, 11 to 13 gallons of distillate fuel [[diesel fuel]] and 3 to 4 gallons of [[jet fuel]] from each {{convert|42|USgal|liter|abbr=off|sp=us}} [[Oil barrel|barrel]] of [[Petroleum|crude oil.]] The product ratio depends upon the processing in an [[oil refinery]] and the [[crude oil assay]].<ref>{{cite web | url=https://www.eia.gov/energyexplained/oil-and-petroleum-products/refining-crude-oil.php | title=Refining crude oil—U.S. Energy Information Administration (EIA) | access-date=27 August 2022 | archive-date=27 August 2022 | archive-url=https://web.archive.org/web/20220827005655/https://www.eia.gov/energyexplained/oil-and-petroleum-products/refining-crude-oil.php | url-status=live }}</ref>